Optical fiber with improved strength in high humidity/high temperature environments

ABSTRACT

A GGP fiber is provided which resists strength degradation upon exposure to high temperature/high humidity environments. The fiber comprises a polymeric coating, or P-coat, which is cured with a photoinitiator such as an iodonium methide salt which does not hydrolyze to release HF or fluoride ion.

REFERENCE TO CROSS-RELATED APPLICATIONS

This application claims priority from U.S. Provisional ApplicationSerial No. 60/167,359, filed Nov. 22, 1999.

FIELD OF THE INVENTION

This invention relates generally to optical fibers, and morespecifically to optical fibers with polymeric coatings.

BACKGROUND

Various types of optical fibers are known to the art. One type ofoptical fiber which is of particular interest is GGP fiber (glass,glass, polymer), so called because it includes a glass core, a glasscladding, and a permanent polymeric coating or P-coat encircling theglass cladding. Optical fiber of this type is commercially availablefrom the Minnesota Mining and Manufacturing Company (3M) under theVOLITION trade name.

A typical GGP fiber construction consists of a glass core, a reducedglass cladding (100 micron), a P-coat (125 micron) and 2 standard buffercoats (the first to provide microbend protection, the second to provideabrasion resistance), such as those available from DSM Desotech (DSM3471-1-152A and 3471-2-136), to give a final diameter of 250 microns. Bycontrast, standard (non-GGP) fiber has a 125 micron glass cladding and 2standard buffer coats (such as the DSM materials listed above) to give afinal diameter of 250 microns.

The P-coat in GGP fiber is a cationically curable system which istypically based on epoxy resins. Other cationically curable resisn arealso known, including those functionalized with cycloaliphatic epoxygroups or vinyl ethers. The P-coat, which typically contains iodoniumhexafluoroantimonate, a cationic photoinitiator, is immediately appliedto the fiber after the fiber is drawn from the furnace and is cured.Typically, one or more protective buffer coats are subsequently appliedand cured over the P-coat to give the final GGP fiber construction.

Various other materials are also known which have been used asphotoinitiators in various processes, materials, and systems, some ofwhich are described below. Of those which have found use in fiber opticapplications, most are radical photoinitiators, since the use ofcationic photoinitiators in this area is still quite limited.

U.S. Pat. No. 5,668,192 (Castellanos et al.) discusses various iodoniumborates as well as organometallic borates as photoinitiators. There isno mention of optical fiber in this patent.

U.S. Pat. No. 5,550,265(Castellanos et al.) discusses organometallicborates as photoinitiators. No mention of optical fiber coating or fiberstrength.

GB 2307473 (Cunningham et al.) discloses organoboron photoinitiators ofthe generic formula G+−B (R₁,R₂, R₃, R₄), wherein G+ can be sulfonium oriodonium and R₁, R₂, R₃ and R₄ are alkyl groups. The photoinitiators aredescribed as being suitable for photopolymerization of compositions withacid groups.

U.S. Pat. No. 4,854,956 (Pluijms et al.) describes a method formanufacturing optical fibers having a core and a cladding of glassapplying a rod-in-tube technique. The reference discusses the use of HFetching solution and its effects on glass. The reference notes that, asfracture points often occur at points of contamination on the glass, HFsolution can be employed to etch the quartz glass tubes. According tothe reference, the conglomerates of alien particles are not attacked orhardly attacked, but the surrounding glass is attacked. After reaching acertain etching depth (10 micron) parts of conglomerates work loose fromthe surface with very low forces, such as the forces created in rinsingaway the etchant.

U.S. Pat. No. 5,448,672 (Blonder et al.) discloses optical fibers withmatte finishes. The authors use mixtures of buffered hydrofluoric acid(e.g., HF and NH₄F) and a treating agent (acetic acid, phosphoric acid,sulfuric acid) to produce a matte finish on optical fibers, for purposesof reduced glare or improved adhesion. The background includes areference to U.S. Pat. No. 4,055,458 which discloses the etching ofglass by means of liquids containing HF.

U.S. Pat. No. 4,655,545 (Yamanishi et al.) discloses a glass fibersuitable for use in optical transmission. The reference discusses anoptical fiber that has been extrusion coated with a fluorine containingresin, which are often found to have a mechanical strength which is muchlower than fibers extrusion coated with non-fluorine containingcoatings. The reference notes that “such a decrease in the mechanicalstrength is ascribed to fluorine gas or HF generated at the time of meltextrusion. More specifically, it is believed that fluorine gas orhydrofluoric acid generated during the extrusion coating passes througha first baked layer and reaches the surface of the glass fibers to erodethe glass surfaces or destroy chemical bonding between the glasssurfaces and the baked layer thereby causing the above-describedreduction in mechanical strength.” The reference proposes the use of anabsorbable solid powder such as titanium oxide, calcium carbonate andthe like to absorb the HF that is generated.

Imides

Methides

Q=H, halogen, CN, R, aryl, Rf, RfSO2, RfCH2OSO2, (Rf)2CHOSO2

EP 834492 discloses the use of ionic compounds, such as those containingpoly iodonium cations, as photoinitiators, although there is no mentionof the application of these materials in coating optical fibers.

EP 775706, U.S. Pat. No. 5,807,905, and WO 9852952 disclosephotoinitiators that have “polyborate” anions.

U.S. Pat. No. 5,554,664 (Lammana et al.) discloses energy activatedsalts with fluorocarbon anions. The reference discusses the advantage ofusing catalysts with non-hydrolyzable anions for adhesives/coatings forelectronics applications, because of the corrosiveness of HF thatresults from the hydrolysis of conventional initiator anions such as PF₆and SbF₆, although the reference does not discuss the application ofthese materials as coatings for optical fibers. The reference focuses onmethide and imide anions in onium salts, and also gives examples ofinitiators with borate anions.

PCT application WO 95/03338 discloses the use of salts of borates aspolymerization catalysts. No reference is made to the use of thematerials described therein in optical fibers.

EP 614958 discloses compositions with cationically crosslinkablepolyorganosiloxane base and the use of these materials in the fields ofanti-adhesion paper, fiber optics and printed circuit protection.Organometallic borate complexes are also disclosed having 4-10 groupswith pi-bonded substituents (mesitlene, mesitylene, toluene etc) andborates with electron withdrawing groups, such as NO₂, F, Cl, or Br.

U.S. Pat. No. 5,468,902 (Castellanos et al.) and U.S. Pat. No. 5,340,898(Cavezzan et al.) discuss iodonium borate salts and cationicallycrosslinkable polysiloxanes.

While GGP fibers have been produced which have many admirable physicaland optical properties, some of these properties have been observed todegrade under certain extreme conditions. In particular, some GGP fibersexhibit a decrease in fiber strength, as shown in dynamic fatigue tests,when they are placed in a high temperature/high humidity environment.Such environments may be replicated in an environmental chamber(FOTP-73) which is cycled from low to high temperatures over a period ofapproximately 10 days.

Unfortunately, such extreme conditions may be encountered by GGP fibersin applications such as avionics, naval or submarine operations, oilfield applications, or even during manufacturing or shipping. Suchconditions may also be encountered outside of the plant in areas where85° C. will likely be an upper specification temperature.

There is thus a need for a GGP fiber which exhibits greater strengthretention after exposure to high temperature/high humidity environments.This and other needs are met by the present invention, as hereinafterdisclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are plots of failure probability rank as a function of failurestress (a Weibull plot) for the optical fibers of the examples.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a GGP fiber whichexhibits greater strength retention after exposure to hightemperature/high humidity cycles. Surprisingly, it has been found thatthe strength retention of fibers exposed to such environments can be toimproved if the P-coat of the fiber is cured with a photoinitiator, suchas iodonium methide, which does not hydrolyze to release HF or fluoride.By contrast, GGP fibers cured with commonly used photoinitiators such assulfonium PF₆ or iodonium SbF₆ which are capable of undergoing such ahydrolysis reaction are seen to suffer significant strength degradationin such environments. A degradation in the strength of a fiber uponexposure to a high temperature/high humidity cycle implies that thefiber will be weaker and may possibly be found to be unacceptable if thefiber is exposed to such an environment.

Detailed Description of the Invention

In accordance with the present invention, a GGP fiber is provided whichexhibits greater strength retention after exposure to hightemperature/high humidity cycles. Such a GGP fiber is achieved byutilizing a P-coat formulation which has a photoinitiator that does nothydrolyze to release HF or fluoride.

The degradation in strength that is often observed in GGP fibers whensuch fibers are exposed to high temperature/high humidity cycles hasheretofore been poorly understood. However, the present investigatorshave found that both environmental components—high temperature and highhumidity—are required for the degradation, since little or no strengthdegradation is observed in fibers exposed to only one of thesecomponents. Thus, for example, fiber exposed to a high temperature/lowhumidity cycle in a FOTP-73 chamber does not exhibit noticeable strengthdegradation.

Degradation in strength implies that the GGP fiber will be weaker andmay perform in an unacceptable manner when the fiber is exposed to theconditions under which strength degradation occurs. The occurrence ofsuch degradation in high temperature/high humidity environments isespecially problematic, since such conditions are frequently encounteredat fiber manufacturing sites.

Without wishing to be bound by theory, it is believed that this strengthdegradation results from hydrolysis of the photoinitiators employed inconventional P-coat compositions. In particular, typical photoinitiatorssuch as iodonium SbF₆ (see below), iodonium PF₆, sulfonium SbF₆, orsulfonium PF₆ initiators are capable of undergoing a hydrolysis reactionunder hot, humid conditions to release HF or F⁻. In the case of SbF₆,for example, the following reaction may occur when the P-coat is exposedto a hot, humid environment:

SbF₆+H₂O=SbF₅OH+HF

The HF generated by this reaction may attack the glass in the fiber or,alternatively, it may attack the epoxy silicone, thereby allowing waterto attack the glass.

In accordance with the present invention, a GGP fiber may be obtainedwhich resists strength degradation in hot and humid conditions byutilizing a photoinitiator in the P-coat formulation which does nothydrolyze to release HF or fluoride. Examples of such photoinitiatorsinclude iodonium salts such as iodonium methide (see above), iodonium—C(SO₂CF₃) ₃, iodonium —B (C₆F₅), and iodonium —N(SO₂CF₃)₂.

One class of materials particularly useful as the anionic portion of theinitiators employed in the present invention may be generally classifiedas fluorinated (including highly fluorinated and perfluoriated) trisalkyl- or arylsulfonyl methides and corresponding bis alkyl- orarylsulfonyl imides, as represented by Formulas 2a and 2b, respectively,and hereinafter referred to as “methide” and “imide” anions,respectively, for brevity:

(R_(f)SO₂)₃C—  (2a)

(R₂SO₂)₂N—  (2b)

wherein each R_(f) is independently selected from the group consistingof highly fluorinated or perfluorinated alkyl or fluorinated arylradicals. The methides and imides may also be cyclic, as when acombination of any two R_(f) groups are linked to form a bridge.

The R_(f) alkyl chains will typically contain from 1-20 carbon atoms,with 1-12 carbon atoms preferred. The R_(f) alkyl chains may be branchedor cyclic, but are preferably straight. Heteroatoms or radicals, such asdivalent oxygen, trivalent nitrogen or hexavalent sulfur, may interruptthe skeletal chain. When R_(f) is or contains a cyclic structure, suchstructure preferably has 5 or 6 ring members, 1 or 2 of which can beheteroatoms. The alkyl radical R is also free of ethylenic or othercarbon-carbon unsaturation, e.g., it is a saturated aliphatic,cycloaliphatic or heterocyclic radical. By “highly fluorinated” is meantthat the degree of fluorination on the chain is sufficient to providethe chain with properties similar to those of a perfluorinated chain.More particularly, a highly fluorinated alkyl group will have more thanhalf the total number of hydrogen atoms on the chain replaced withfluorine atoms. Although hydrogen atoms may remain on the chain, it ispreferred that all hydrogen atoms be replaced with fluorine to form aperfluoroalkyl group, and that any hydrogen atoms beyond the at leasthalf replaced with fluorine that are not replaced with fluorine bereplaced with bromine and/or chlorine. It is more preferred that atleast two out of three hydrogens on the alkyl group be replaced withfluorine, still more preferred that at least thee of four hydrogen atomsbe replaced with fluorine, and most referred that all hydrogen atoms bereplaced with fluorine to form a perfluorinated alkyl group.

The fluorinated aryl radicals of Formulas 2a and 2b may contain from 6to 22 ring carbon atoms, preferably 6 ring carbon atoms, where at leastone, and preferably at least two, ring carbon atoms of each aryl radicalis substituted with a fluorine atom or a highly fluorinated orperfluorinated alkyl radical as defined above, e.g., CF₃.

Specific examples of anions useful in the practice of the presentinvention include: (C₂F₅SO₂)₂N—, (C₄F₉SO₂)₂N—, C₈F₁₇SO₂)₃C—,(CF₃SO₂)₂N—, C₄F₉SO₂)₃C—, (CF₃SO₂)₂(C₄F₉SO₂)C—, (CF₃SO₂)(C₄F₉SO₂)N—,[(CF₃) ₂NC₂F₄SO₂N—, (CF₃)₂NC₂F₄SO₂C—(SO₂CF₃)₂, (3,5-bis(CF₃)C₆H₃)SO₂N—SO₂CF₃, and the like. More preferred an those described by Formula 2a,wherein R is a perfluoroalkyl radical having 1-4 carbon atoms. Anions ofthis type, and methods for making them, are described in U.S. Pat. No.4,505,997, U.S. Pat. No. 5,021,308, U.S. Pat. No. 4,387,222, U.S. Pat.No. 5,072,040, U.S. Pat. No. 5,162,177, and U.S. Pat. No. 5,273,840, andin Turowsky and Seppelt, Inorg. Chem., 27, 2135-2137 (1988). Turowskyand Seppelt describe the direct synthesis of the (CF₃SO₂),C— anion fromCF₃SO₂F and CH₃MgCl in 20% yield based on CF₃SO₂F (19% based onCH₃MgCl). U.S. Pat. No. 5,554,664 describes an improved method forsynthesizing iodonium methide.

Salts of the above described anions may be activated by radiation or byheat or may require two stage activation involving radiation followed byheat. Suitable salts having such non-nucleophilic anions for use asphotoinitiators in the polymeizable P-coat compositions of the instantinvention are those salts that upon application of a sufficientenergy-thermal, an accelerated particle beam (electron beam), orelectromagnetic radiation having a wavelength from about 200 to 800 nm,will generate reactive species capable of initiating or catalyzing thepolymerization of the P-coat compositions.

A typical GGP fiber construction made in accordance with the inventionconsists of a glass core, a reduced glass cladding (100 micron), aP-coat (125 micron) and 2 standard buffer coats (the first to providemicrobend protection, the second to provide abrasion resistance), suchas those available from DSM Desotech (DSM 3471-1-152A and 3471-2-136),to give a final diameter of 250 microns. However, the present inventionis not limited to a particular fiber construction. Thus, otherconstructions are also contemplated for use in the present inventionwhich have varying individual layer thicknesses or total fiberdiameters. The diameter of the glass core may also be varied, dependingon whether the fiber is intended for single mode use (in which case thecore diameter is typically about 8 microns) or multimode (in which casethe core diameter will typically be about 50-62 microns). Typically,thinner fibers are found to experience greater strength degradation in ahot, humid environment, since there is a smaller glass diameter to startwith.

OPTICAL FIBERS AND PRE-FORMS

The following is a description of the optical fibers and pre-formsreferred to in the examples.

GGP3.1—a P-coat formulation consisting of 95% resins and 5% of aphotoinitiator. The resins are a 42:58 ratio of Epon 828 (a bisphenoldiglycidyl ether resin available commercially from Shell Chemical Co.,Houston, Tex., and GP554 (a silicone with a high level of epoxyfunctionality, available commercially from Genesee Polymers Inc., FlintMich.

GGP3.2—a P-coat formulation having the same composition as GGP3.1,except that the ratio of Epon 828: GP554 is 60:40.

TESTS AND PROCEDURES

The following is a description of the tests and procedures that arereferred to throughout the present application.

PREPARATION OF FIBER OPTIC PRE-FORM

The fiber optic pre-forms used in the following examples were preparedin accordance with the methods described in U.S. Pat. No. 4,217,027(MacChesney et al.), which is incorporated herein by reference.

FIBER DRAWING PROCESS

The fiber optic draw tower used in the draw process was based on anenclosed Nokia system which featured a Nokia-Maillefer fiber draw tower(Vantaa, Finland). To begin the draw process, a downfeed system was usedto control the rate at which the optical pre-form was fed into a 15KWLapel Zirconia induction furnace (Lapel Corp., Maspeth, N.Y.) in whichthe pre-form was heated to a temperature at which it may be drawn to afiber (between 2200 to 2250° C.). Below the heat source, a LaserMike™laser telemetric measurement system was used to measure the drawn fiberdiameter as well as monitor the fiber position within the tower.

The newly formed fiber was then passed to a primary coating station atwhich the protective coating was applied. The coating station included acoating die assembly, a Fusion Systems R Corp. microwave UV curingsystem, a concentricity monitor, and another laser telemetric system.The coating die assembly, based on a Norrsken Corp. design, consisted ofa sizing die(s), back pressure die and a containment housing which wasmounted on a stage having adjustment for pitch and tilt and x-ytranslation. These adjustments were used to control coatingconcentricity. The protective coating material was supplied to thecoating die assembly from a pressurized and was applied, cured andmeasured within the primary coating station.

The coated fiber then proceeded to a secondary coating station where abuffer was applied to the coated fiber. In certain cases it wasdesirable to apply two buffer layers simultaneously in a wet-on-wetapplication at the secondary coating station. In this case an additionalsizing die as used and an additional vessel was used to supply materialto this die. The coatings were applied, one after the other, and thencured and outer diameter measured. As required, additional coatingscould be applied via additional coating stations. Ultimately, thecompleted optical fiber element was drawn through a control capstan andonto a take-up spool (Nokia).

DYNAMIC FATIGUE TESTING PROCEDURE

With the following noted exceptions, this test was performed inaccordance with Fiber Optic Test Procedure (“FOTP”) 28, entitled “Methodfor Measuring Dynamic Tensile Strength of Optical Fiber”, and numberedEIA/TIA-455-28B (Revision of EIA-455-28A), where EIA stands forElectronic Industries Association and TIA stands for TelecommunicationsIndustry Association. The exceptions are as follows:

Strain rate=9% per minute

Gage length=4 meters

Environment=Ambient laboratory.

FIBER OPTIC TESTING PROCEDURE (FOTP 73)

FOTP 73 is a test in which samples of fiber are placed in a programmablechamber capable of wide ranges in temperature and humidity (the T_H orT/H test of the title). Typically, instrumentation monitors thewavelengths travelling through the fiber in response to the changingenvironment. The samples are exposed to a maximum temperature of 85° C.with a relative humidity of 98% and a minimum temperature of −10° C.with a relative humidity of 25%. Each stopping point is approximately 3hours and the test is run for 10 days. The fiber samples see the extremeconditions of 85° C. and 98%RH for 42 hours.

In the following examples, the fiber's dynamic tensile strength was thenmeasured per FOTP 28, although this measurement is not part of the FOTP73. It is to be noted that, in conducting the temperature/humidity test,the fiber is wound on a quartz spool or collapsible aluminum spool, bothof which differ from a standard thermoplastic storage spool, the laterbeing unsuitable for the high temperatures experienced during the test.Quartz glass expands at the same rate as the fiber, so no extra stressis applied to the fiber during the environmental test simply due tospool expansion. The collapsible aluminum spools were developed asconvenient, inexpensive, durable, small alternatives to the quartzspools. The fiber is wound on the spools which are then collapsed sothat the fiber hangs loosely.

COMPARATIVE EXAMPLE 1

An optical fiber pre-form was prepared in accordance with thePREPARATION OF FIBER OPTIC PRE-FORM PROCESS. Pat. No. The pre-form wassubsequently drawn in accordance with the FIBER DRAWING PROCESS, duringwhich a P-coat was applied that was cured with iodoniumhexafluoroantimonate photoinitiator.

COMPARATIVE EXAMPLE 2

The fiber of COMPARATIVE EXAMPLE 1 was divided into 20 pieces ofapproximately equal length, and each of the 20 pieces was then subjectedto the DYNAMIC FATIGUE TESTING PROCEDURE. The results are depictedgraphically in FIG. 1 as CURVE A.

COMPARATIVE EXAMPLES 3-5

Three additional optical fibers were prepared in accordance withCOMPARATIVE EXAMPLE 1. The resulting fibers, which are referred tohereinafter as COMPARATIVE EXAMPLES 3-5, were identical except for minorvariations caused by normal fluctuations in manufacturing processparameters. Each fiber was then exposed to the conditions of the FIBEROPTIC TESTING PROCEDURE and was then analyzed by way of the DYNAMICFATIGUE TESTING PROCEDURE in order to ascertain the effect of a hightemperature/high humidity environment on fiber strength. The results ofthe DYNAMIC FATIGUE TESTING PROCEDURE for COMPARATIVE EXAMPLES 3-5 aredepicted as a Weibull distribution in FIG. 1 as CURVES B, C, and D,respectively.

As shown in FIG. 1, the fibers of COMPARATIVE EXAMPLES 3-5 clearlyexhibit a strength degradation after thermal humidity cycling ascompared to the fiber of COMPARATIVE EXAMPLE 1 which, though of the samecomposition, was not subjected to the thermal humidity cycle.

EXAMPLE 1

A fiber was prepared in accordance with the methodology of COMPARATIVEEXAMPLE 1, except that the P-coat formulation was GGP3.2 which was curedwith an iodonium methide photoinitiator. The fiber was divided into 20pieces of approximately equal length, and each of the 20 pieces was thensubjected to the DYNAMIC FATIGUE TESTING PROCEDURE. The results aredepicted graphically in FIG. 2 as CURVE E.

EXAMPLES 2-5

Three fibers were prepared in accordance with the methodology ofEXAMPLE 1. The resulting fibers, which are referred to hereinafter asEXAMPLES 2-5, were identical except for minor variations caused bynormal fluctuations in manufacturing process parameters.

Each fiber was then divided into 20 pieces of approximately equallength, was exposed to the conditions of the FIBER OPTIC TESTINGPROCEDURE, and was then analyzed by way of the DYNAMIC FATIGUE TESTINGPROCEDURE in order to ascertain the effect of a high temperature/highhumidity environment on fiber strength. The results of the DYNAMICFATIGUE TESTING PROCEDURE for EXAMPLES 2-5 are depicted as a Weibulldistribution in FIG. 2 as CURVES F, G, H, and 1, respectively.

In contrast, the graph below compares the dynamic fatigue of GGP3.2fiber cured with the iodonium methide photoinitiator. There is nodegradation in strength upon exposure of the fiber to the hightemperature/high humidity environmental chamber.

COMPARATIVE EXAMPLES 6-8

The following examples illustrates the tendency of various P-coatformulations containing photoinitiators to hydrolyze so as to generatefluoride ion in a humid environment.

Two samples of P-coat formulations cured with different photoinitiatorswere provided in film form. In COMPARATIVE EXAMPLE 6, the film wasGGP3.2 cured with 5% UVI 6974 sulfonium SbF₆, a photoinitiator which iscommercially available from Union carbide. In COMPARATIVE EXAMPLE 7, thefilm was GGP3.2 cured with 5% UVI 6990 sulfonium PF6 photoinitiator(also available commercially from Union Carbide). In COMPARATIVE EXAMPLE8, the film was GGP3.2 cured with iodonium SbF₆ photoinitiator.

A hot-water extraction method was used to transport the fluoride fromthe sample into aqueous solution, and a DX-500 Ion Chromatography systemwas used to analyze the fluoride content in that solution. The sampleswere weighed into PTFE cups and 10 ml of ultra-pure water added bypipette. The cups were then covered with a PTFE cap, placed into astainless steel bomb cylinder and heated at 105° C. for a period of 20hours. This procedure was completed in triplicate for each sample.Fluoride analyses of the samples were carried out using a Dionex DX 500Ion Chromatography system (consisting of a GP40 quaternary gradientpump, AS3500 Autosampler, SRS Self-Regenerating Chemical suppressor, andan ED40 Electrochemical Detector with a conductivity cell). A DionexIonPac AS14 anion exchange column (IonPac AG14 guard column) and 4.8 mmsodium carbonate/0.6 mm sodium bicarbonate eluent was employed toperform the separation. The mobile phase was delivered at a flow rate of1.2 ml/min. The analysis used a 50 μL injection for sample and standardsolutions. The standards ranged from 0.01-10 ppm.

The results are reported in TABLE 1 as parts per million fluoride, andare an average of the replicates with the error range being the standarddeviation.

TABLE 1 EXAMPLE Fluoride Concentration (ppm) COMPARATIVE EXAMPLE 6 735.3(+/−83) EXAMPLE 6  12.6 (+/−2) COMPARATIVE EXAMPLE 7 246.9 (+/−46)EXAMPLE 7 <0.8 COMPARATIVE EXAMPLE 8 395.5 (+/−90) EXAMPLE 8 <3.1

EXAMPLES 6-8

The experiment of COMPARATIVE EXAMPLES 6-8 was repeated using similarp-coat compositions made from photoinitiators which are not capable ofhydrolyzing to generate fluoride ion. The film of EXAMPLE 6 was GGP3.2cured with 5% PC702 iodonium “borate” photoinitiator, a photoinitiatorwhich is commercially available from Rhodia or Rhone-Poulenc. The filmof EXAMPLE 7 was GGP3.2 cured with 5% iodonium “imide” photoinitiator.The film of EXAMPLE 8 was GGP3.2 cured with iodonium methidephotoinitiator.

As indicated by the results in TABLE 1, the films generated from p-coatformulations containing photoinitiators that are capable of hydrolyzingto generate fluoride ion were observed to undergo such a hydrolysis. Bycontrast, far lower fluoride ion concentrations were observed with theP-coat formulations that did not contain such photoinitiators. Theseresults strongly correlate with the strength of the respective fibersafter exposure to hot/humid environments. Initiators that generateextractable fluoride lead to fibers that degrade in strength, whileinitiators that do not yield significant extractable fluoride maintainhigh strength.

The preceding description of the present invention is merelyillustrative, and is not intended to be limiting. Therefore, the scopeof the present invention should be construed solely by reference to theappended claims.

What is claimed is:
 1. An optical fiber, comprising: a glass core; aglass cladding; and a polymeric coating, comprising a photoinitiatorthat does not hydrolyze to release HF or fluoride ion.
 2. The opticalfiber of claim 1, wherein said glass cladding is disposed on said glasscore.
 3. The optical fiber of claim 1 or 2, wherein said polymericcoating is disposed on said glass cladding.
 4. The optical fiber ofclaim 1, wherein said photoinitiator comprises an organic cation and ananion, and wherein said anion is devoid of fluorine.
 5. The opticalfiber of claim 1, wherein said photoinitiator comprises an organiccation and an anion, and wherein any fluorine atoms in said anion arecovalently bonded to carbon.
 6. The optical fiber of claim 1, whereinsaid photoinitiator is a salt having an anion selected from the groupconsisting of methides, imides, and borates.
 7. The optical fiber ofclaim 6, wherein said photoinitiator is a salt having a methide anion.8. The optical fiber of claim 1, wherein said photoinitiator is a salthaving an anion selected from the group consisting of —C(SO₂CF₃)₃, —B(C₆F₅), and —N(SO₂CF₃)₂.
 9. The optical fiber of claim 1, wherein saidphotoinitiator is a salt having an onium cation.
 10. The optical fiberof claim 9, wherein said cation is selected from the group consisting ofiodonium cations and sulfonium cations.
 11. The optical fiber of claim1, wherein said photoinitiator is selected from the group consisting of:iodonium methide, iodonium —C(SO₂CF₃)₃, iodonium —B (C₆F₅), and iodonium—N(SO₂CF₃)₂—.
 12. The optical fiber of claim 1, wherein saidphotoinitiator is iodonium methide.
 13. The optical fiber of claim 1,wherein said photoinitiator is iodonium salt having the anion —B (C₆F₅).14. The optical fiber of claim 1, wherein said photoinitiator isiodonium —N(SO₂CF₃)₂—.
 15. The optical fiber of claim 1, wherein saidphotoinitiator is an iodonium salt having the anion —C(SO₂CF₃)₃.
 16. Theoptical fiber of claim 15, wherein said photoinitiator is bis dodecylphenyl iodonium tris trifluoromethyl sulfonyl methide).
 17. An opticalfiber element, comprising: an optical fiber having a numerical apertureranging from 0.08 to 0.34; and a protective coating affixed to the outersurface of said optical fiber, said protective coating having a Shore Dhardness value of at least 65; wherein said protective coating comprisesa photoinitiator that does not hydrolyze to release HF or fluoride. 18.The optical fiber element of claim 17, wherein said photoinitiator is aniodonium methide salt.
 19. An optical fiber, comprising: a glass core; aglass cladding, disposed about said core; and a polymeric coatingdisposed on said cladding, said coating comprising a photoinitiatorhaving a non-hydrolyzable anion.